1. Field of the Invention
The invention relates to a servobrake for motor vehicles.
2. Description of the Related Art
The invention relates to a servobrake for motor vehicles with a booster housing the interior of which is subdivided by a movable wall into a vacuum chamber and a working chamber, and with a control housing carrying the movable wall, in which control housing is arranged a control valve which controls a pneumatic pressure difference acting on the movable wall, can be actuated both by an actuating rod by means of a valve piston, and also, independently of the actuating rod, by an electromagnet, and consists of three seal seats arranged concentrically with respect to one another and of a valve body which cooperates with the seal seats and is provided with axial passages, the first seal seat being formed in the control housing and the second seal seat on the valve piston, while the third seal seat is formed on a sleeve cooperating with the electromagnet, there being provided an annular element which is arranged displaceably with respect to the third seal seat and which bears against the sleeve via an interposed elastic or compressible element, the edge region of which annular element oriented towards the valve body has partial areas separated from one another by radial openings via which it is in contact with the valve body, and which edge region in the release position is arranged axially offset towards the valve body with respect to the third seal seat, the annular element being arranged radially inside the sleeve in such a manner that its partial areas, by which it is in contact with the valve body, at least partially open the passages provided in the valve body.
A servobrake of this type is known from WO 2006/005742 A1. However, in the known servobrake noises which are experienced as disturbing occur in normal braking operation. This negative noise behavior is explained by the sudden reversal of the air flow against edges of the sleeve and by swirl of the incoming air flow against the second seal seat in the direction of the working chamber as a result of one-sided lifting of the second seal seat from the valve body, the swirl causing a vibrating air column to be produced in a chamber of the valve body. It is further regarded as negative that the swirl has a negative influence on the response-time and release-time dynamics of the servobrake.